Thermostatic control device



May 14, 1957 HAwKE 2,792,473

THERMOSTATIC CONTROL DEVICE Filed Jan. 20, 1954 Z2 a z 28 i 48 /4 ;4

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FIG 5 INVENTOR. FRANK 7. HAW/(f BY M M,f lz;- vm

ATTORNEYS.

United States Patent O THERMOSTATIC CONTROL DEVICE Frank T. Hawke,Paris, Ky., assignor to ElectrioSteam Radiator Corporation, Paris, Ky.,a corporation of Michigan Application January 20, 1954, Serial No.405,215

7 Claims. (Cl. 200-138) This invention relates to a thermostatic controlfor an electrical circuit and is especially concerned with a controlemploying a bimetal heat responsive element to actuate an electricswitch.

An exemplary application of the invention lies in thermostaticallyclosing and opening a circuit for an electrical appliance such as aspace heating device. It is a primary object of this invention toprovide a thermostat structure which is durable yet simpler and lessexpensive of manufacture than structures now known in the art.

The invention is carried out in part by utilizing the inherentresiliency of the bimetal heat responsive element in such a way as toeliminate the necessity for additional spring structure to maintainproper contact between the bimetal element and a switch and a regulatorelement. Another part of the invention is carried out by so adapting thebase of the device that lead-in wires are clamped in position betweenthe base and the casing of the switch thereby eliminating the necessityfor special anchoring or stabilizing structure for the leads. Two formsof the invention are shown in the accompanying drawings which may bebriefly described as follows:

Fig. l is a plan view of the device of this invention illustrating therelation of the various parts.

Fig. 2 is a sectional view taken on line 22 of Fig. 1.

Fig. 3 is a sectional view taken on line 3-3 of Fig. 1.

Fig. 4 is a plan view of a modified form of the invention.

Fig. 5 is a sectional view taken on line 5-5 of Fig. 4.

The device shown in the drawings has a body comprised of a base 12 and acover 14. A micro-switch 16, which may be of a generally availablecommercial type, is secured to the base 12 by such means as screws 18.Also mounted on the base 12 and spaced from the switch 16 is a shiftableregulator element 20 which is preferably in the form of a rotatable camas shown. The regulator cam has an operating stem 22 extending throughan opening in the cover 14 and having at its outer end an operating knob24 with a flange 26 graduated to indicate temperature settings.

A heat responsive bimetal element 28 having two layers of metal 30 and32 with unlike thermal expansion characteristics is mounted on the base12 in the manner of a beam with one end portion engaging the regulatorcam 20 and its other end portion engaging the actuator button or plunger34 of the switch 16. The mounting for the bimetal element liesintermediate the switch and the regulator cam and comprises simply asingle stud 36 secured to a projection 38 on the base and to the bimetalelement. The stud 36 may advantageously comprise an ordinary screw asshown. The bimetal element preferably has a simple, generally flatplate-like form.

The mounting is arranged to hold the bimetal element in stressedcondition for all operative positions of the regulator cam 20. Theplunger 34 is biased outwardly by a spring in the micro-switch, which isstrong enough to hold the bimetal element in stressed condition, butwhich yields to heat responsive flexing movements there- 7 2,792,413Patented M Y g 9 7 of. The micro-switch is very sensitive, being openedand closed by slight movements of the bimetal element 28 and plunger 34.The base 12 has knife-edged projections 40 engaging the sides of thebimetal element 28 and preventing it from pivoting on the stud 36 duringuse.

The base 12 has portions 42 which provide seats for the casing of themicro-switch (Fig. 2). The base also has recessed means as shown at 44to contain the leadin wires or cable 46. The recess 44 is relativelyshallow so that when the switch 16 is secured to the base 12 the lead-incable 46 is firmly clamped between the switch casing and the walls ofthe recess, as illustrated in Fig. 2. This structure eliminates thenecessity of providing a special clamp for stabilizing the lead-in wireswithin the thermostat body. I

In use, the parts are assembled as described above with the lead-inWires'connected to the terminals 48 "on the switch 16. To place thethermostat in its oil? position, the control knob 24 is turned so thatthe flat face 59 of the cam is opposed to the bimetal element 28. ln

1 this position, the stress in the bimetal element and the pressureexerted thereby on the plunger 34 are relieved; the plunger is inretracted position, and while the bimetal element may respond totemperature changes, it will not actuate the plunger.

The thermostat is placed in operative position by turn ing the controlknob 24 to bring the rounded portion of the regulator cam 20 intoengagement with the bimetal element 28 (Fig. 1). The bimetal element isthus stressed, the stud 36 acts as a fulcrum and the plunger 34 isdepressed. The thermostat is set to operate at a selected temperature byturning the control knob 24 to the proper setting as indicated on thegraduated flange 26. Turning the control knob shifts the cam 20 andvaries the stress in the bimetal element 28 which in turn varies theamount of heat responsive flexure required of the bimetal element toactuate the plunger and operate the switch. The thermostat is turned offby returning the control knob to the ott position described above.

The screw 36 provides for a fine adjustment of the ress in the bimetalelement and thus provides calibrating means for the graduated flange 26.

In the modified form of the invention shown in Figs. 4 and 5, a bimetalelement 60 is secured to a bracket 62 which is pivoted on the base 64 bysuch means as a pintle or bolt 66. In this form of the invention thestabilizing projections 40 are not needed and are omitted. A screw 68 isthreaded through the bimetal element and engages the regulator cam 20 toprovide for the fine adjustment of stress in the bimetal element.

I claim:

1. A thermostatic control device having a base and an encased electricswitch and switch actuator means mounted on the base, said base havingrecessed means adapted to receive electric lead wires connected to theswitch, and means securing the switch casing to the base with a portionof the switch casing firmly engaging lead wires in said recess wherebyto secure the lead wires to said device.

2. In a thermostat of the type having switch means and a regulatorelement operably interconnected by a heat responsive bimetal element,structure comprising a body, a heat responsive bimetal element havingsubstantially flat form throughout its entire extent, mounting meanssecuring a generally central portion of said element on said body withboth end portions of said element being free, spaced apart switch meansand regulator means on said body, one of the free end portions of saidbimetal element operably engaging said switch means and the other freeend portion of said element operably engaging said regulator means, sothat said element extends between said switch means and regulator means3 as a generally fiat, simple beam, said parts being arranged so thatsaid mounting means imposes a generally central load on said beam.

3. The structure defined in claim 2 wherein said mounting meanscomprises a stud transfixing a generally central portion of said bimetalelement and being secured on said body.

4. The structure defined in claim 2 wherein said mounting meanscomprises, a projection on said body, a single screw extending through ahole in a generally central portion of said element, said screw beingthreadedly secured to said projection and thereby forming calibratingmeans for said regulator means.

5. The structure defined in claim 4 characterized in that said body hasanother projection on each side of the first mentioned projection, saidother projections en- .gaging'edge portions of said bimetal element tosupport the same against pivotal movement about the axis of said screw.

6. The structure defined in claim 2 wherein said mounting meanscomprises, a bracket secured to a generally central portion of one faceof said element, said bracket being pivotally mounted on said body, theaxis of the pivotal mounting being generally parallel to said face ofsaid element.

7. In a thermostat of the type having switch means and a regulatorelement operably interconnected by a heat responsive bimetal element,structure comprising, a body, spaced apart switch means and regulatormeans on said body, a heat responsive bimetal element havingsubstantially fiat form throughout its entire extent, one end portion ofsaid bimetal element operably engaging said switch means and the otherend portion of the element operably engaging said regulator means sothat said element extends between said switch means and regulator meansas a generally fiat simple beam, and means fixing a generally centralportion of said element relative to said body, said means securing saidelement against movement in its plane relatively to said body whileenabling said element to flex responsively to loads imposed thereon atsaid switch means and regulator means.

References Cited in the file of this patent UNITED STATES PATENTS2,111,347 Wheat Mar. 15, 1938 2,111,816 Shaw Mar. 22, 1938 2,514,559Riemenschneider July 11, 1950 2,613,298 Armstrong Oct. 7, 1952

